Centralized traffic controlling system for railroads



5, 1939. w. T. POWELL I I ,479.,

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR HAILROADS Filed May 28, 1957a Sheets-Sheet 1 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS w.T. POWELL Filed May 28, 1937 6 Sheets-Sheet 2 INVENTOR BY 10.1 Wnwd,

MW fi ATTORNEY Aug. 15, 1939. w, POWELL 2,169,479

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May 28, 19376 Sheets-Sheet 5 r 20 5 3 6:2 E 3 3 a ATTORNE'Y om 3 Gm L 9 T Y Sui m2 Emm It Aug. 15, 1939. w ow 2,169,479

CENTRALIZED TRAFFIC CONTROLLING SYSITEM FOR RAH-ROADS 6 Sheets-Sheet 5Filed May 28, 1957 m CLUPQNP I |t| IIL in M II guscou 32.0 0233 9:32am m200 3.35. icSEU 5. L an own 1 m 05m 1||| l 3:6 n co uu icH oh P i amv2-3 L N t. at

INVENTOR ATTORNEY Aug. 15, 1939. w. T. POW ELL 2,169,479

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR BAILROADS Filed May 28, 19376 Sheets-Sheet 6 INVENTO 10.1-

ATTORNEY.

I Y b I cMWdM J n". hoi BUJ Lo unzomEou Patented Aug. 15, 1939 UNITEDSTATES PATENT OFFIQE CENTRALIZED TRAFFIC CONTROLLING SYSTEM FORRAILROADS Winfred T. Powell, Brighton, N. Y., assignor to GeneralRailway Signal Company, Rochester, N, Y.

Application May 28, 1937, Serial No. 145,323

4 Claims. (01. 177-353) This [invention relates to centralized trafiicline repeater relay, as will be pointed out in controlling systems forgoverning traffic on raildetail in the following description. roads, andit more particularly pertains to the Still another object of the presentinvention is communication part of such systems. the lockout arrangementprovided at the field I In centralized traihc controlling systems of thestations, whereby the lookout function is effec- 5 type contemplated bythis invention, the switchtive during the first deenergization of theline es and signals are distributed at field stations circuit at thebeginni g o a Cycle initiated o throughout the territory and aregoverned from the field station, that is, only a very short inthecontrol oflice by means of the transmission terval of time is requiredto provide the lookout of controls over a two-wire line circuitinterconfunction and this time is that which is also 10 meeting thecontrol o ifice with the several field p o ed initiating the y e 1 as Wbe stations. Indications relating to the condition e plained n d a la inthe descriptionof the switches and signals, as well a track oo A furtherfeature of the present invention is cupancy and unoccupancy conditions,are transthe Provision o a line r p Stick relay at 15 mitted over thesame two wire line circuit to each station, pe n w the pp n 15 th ntr lffioe lays for checking the response of the stepping re- The two linewires connecting the control ofiioe lays before the circuit condition ischanged to with all of the field stations comprise a single effect the erequired pcircuit, which serves the purpose of carrying. the Another eture of the present invention re- 7 impulses used to select the requiredstation and sides in the manner in Which iYIdiCatiOhS are 20 fortransmitting controls to the selected station, transmitted from atransmitting field a on to as well as carrying the impulses used toidentify a the Control by means of polar impulses calling station in theofiice and transmitting inapplied t the line u the p y of Which di ationth f om, is determined at the field station from energy The presentinvention is of the station selecppli d to the i circuit in the controlofficc, as 25 tion coded simplex type, that is, the system is Will be pfi y p ed out late in the deoperated through cycles during each of whicha scrip stati n: selection trol cod may b t Still another feature of thepresent invention mitted, followed by the transmission of controlresides in e ma ner in Which a rectifier or c de t th l t d st tion,valve at the transmitting field station is con 30 For the transmissionof controls, a predeternetted in the line circuit; to allow (-1-) energymined number of impulses of selected polarities Which is first appliedto e l n the control are placed on the line circuit for operating the fit0 find a p through the a sm step-by-step apparatus in the control fn ad station or not; and if the rectifier is so connected at the fieldstations in synchronism thr ugh cyin the line that current is notallowed to fiow in 35 cles of operations, irrespective of the polarityresponse t0 the energy pp e ther o, the of the impulses. The distinctivepolarity of the Office c a ges to a ener i t on. impulses of each seriesmake up a code combina- A further feature of the present invention, tionwhich determines the particular station to s own as a modification,resides in prov an be selected and the controls to be transmittedOver-balance or an under-balance in a Wheat- 40 therebo stone bridgecircuit, one arm of which includes One feature of the present inventionresides in the line circuit for operating a polar line relay in themanner in which the line circuit apparatus is fi Office t Q F or anotherfor selecchecked or locked in its energized or deenerllely recelvmgmdlcatmns' Another important feature of the present inglzed cendmon mmthe apparatus affected by vention resides in a compensating arrangementthe energization and deenergization of the line for maintaining the linecircuit in approximate respondsbalance when the communication system isin a Another feature of the present invention re- Condition of rest, S0that the proper 'margihs do sides in the circuit arrangement providedfor may be provided f r the ovehbalahoeand d check ng t e Continuity ofthe Circuits including balance, in accordance with the indications to bethe channel circuits which select the code jumpt an mitted, ers and thecontrol relays at selected stations, to A further feature of the presentinvention remaintain the station selecting relay circuit comsides inthe. provision of a pair of thyratron plete and'to provide a circuit forenergizing the tubes, or tubes of the gas filled, arc discharge 55 type,for selectively detecting the over-balance and the under-balancecondition of the line circuit in. accordance with indications to betransmitted.

These characteristic features of the present invention thus brieflystated, and other features of the present embodiment will be explainedwill be made to the accompanyingv drawings, in

whichthose parts having'similar features and functions are designatedthroughout the drawings by like letter reference characters; which* aregenerally made distinctive either by reason of distinctive exponentsrepresentative 'of their location in the system, or by means ofpreceding numerals representative of their order of operation during acycle and in which:-

Figs. 1A and 1B (with Fig. 1A placed above Fig. 1B and withcorrespondingly numbered lines in alignment), illustrate the apparatusand circuit arrangement of the preferred form of the present invention,employed in the control ofiice for providing means whereby the operatormay select the, stations and govern the switches and signals at theselected stations; and also for pro viding means whereby indications maybe received from the various field stations throughout the territory.

Figs. 2A and 23 (with Fig. 2B placed below Fig. 2A and withcorrespondingly numbered lines in alignment), illustrate the apparatusand circuit arrangement employed at a typical field station forreceiving the polar control impulses applied to the line circuit, forcausing the station stepping mechanism'to operate in synchronism withthe ofiice stepping mechanism and for providing the control codecombinations. Figs. 2A and 23 also illustrate the apparatus and circuitarrangement employed at the field station for providing for thetransmission of indications to the control ofiice.

Fig. 3 illustrates a small'portion of the apparatus and circuitsemployed in the control office and at the field station for transmittingand receiving indications by means of the over-rbalance andunder-balance Wheatstone bridge method. The circuits and apparatusillustrated in Fig. 3 represent certain modifications of similarapparatus shown in the preferred embodiment and it will be laterexplained how the preferred arrangement is modified to provide theoperation obtained in the Fig. 3 modification.

Fig. 4 illustrates the apparatus and circuits applied'to the linecircuit of the over-balance and under-balance Wheatstone bridgearrangement, whereby a compensator maintains the resistance value of theline at an approximate fixed value, by adjusting the value of acompensating resistance in the control office, up or down, during thenormal condition of the communication system.

Figs. 5, 6 and 7 illustrate the different conditions of the linecircuit, shown in schematic form for the purpose of obtaining a betterpicture of the circuit arrangement of Figs. 3 and 4 under variousconditions. 7

Fig. 8 illustrates the apparatus and circuit arrangement employed forreceiving indications by the over-balanced and under-balancedWheatfeatures stone bridge method, by the use of gas filled, arcdischarge tubes.

For the purpose of. simplifying the drawings and facilitating in theexplanation, various parts and circuits have been diagrammatically shownand certain conventional illustrations have been employed. For example,the various relays and their contacts are illustrated in a conventionalmanner and symbols are used to indicate the connections to the terminalsof batteries or other sources of current, instead of showing all of thewiring connections to these terminals. Furthermore, the circuit foroperating relay CD in Fig.

1A is not shown in detail, since it is immaterial just how this relay iscontrolled for an understanding of the present invention.

The symbols and are employed to indicate the positive and negativeterminals, respectively, of suitable batteries or other sources ofdirect current and the circuits with which these symbols are used alwayshave current flowing in the same direction, that is, from to I Thesymbols (3+) and (B) are employed to indicate the positive and negativeterminals respectively of a suitable battery or other source of current,having a mid-tap (CN) and the circuits with which these symbols are usedhave current flowing in one direction or another, in accordance withwhether the connection is to be (3+) or (B). a I

The detailed circuit arrangement and the op:- eration of the presentsystem may be more readily understood by considering the drawings, inconnection with typical operations explained in detail in thespecification.

Control oflice equipment.-The control ofiice' includes a control machinehaw'ng a group of control levers for each field station, only one ofwhich (SML) is shown in Fig. 1A, since the control transmitted by otherlevers, when pro; vided, Will be understood from the typical example tobe described with respect to the operation controlled in accordance withthe position. of lever SMEL. The customary miniature track layout,corresponding to the actual track layout in the field, together with thevarious indicating lamps, or the like, and the apparatus and circuitsrequired to accomplish the desired func tions with which this apparatusis related, all have been omitted from the present drawings for the sakeof simplicity.

Each group of control levers representing a field station has associatedtherewith a starting button STB, a change relay CH and a codedetermining relay CD which cooperate with relays C, LC and CD8 common toall the groups to initiate the system into operation. For example, codedetermining relay CD selects jumpers I3 and I4, as well as lever SML,and is picked up when the system is at rest if its relay CH is pickedup. Similarly, each of the other code determining relays (not shown) arecontrolled by their respective relays OH to select the code jumpersandcontrol levers of their station, all

are for the purpose of applying positive and negative impulses to theline circuit in accordance with the control code required. Line relay Fis of the biased-to-neutral polar type and, since it is connected inseries with the line circuit, it responds to the impulses applied to theline circuit by positioning its polar contacts to their neutralpositions when the line is deenergized, to their right-hand positionswhen the line is energized with a positive impulse and to their lefthandpositions when the line is energized with a negative impulse.

Line repeating relay FP repeates the impulses applied to the linecircuit from the control oflice, this relay following the operations of.line relay F during each control cycle. Slow acting relays SA and SB andquick acting relay SC are for the purpose of defining the bounds of anoperating cycle, that is, these relays are all picked up during theconditioning period at the beginning of a cycle, are held up during theimpulsing periods of the cycle and are released during the clearing outperiod at the end of the cycle. Relay SA is again picked up after theclearing out period, when the system is restored to normal and remainspicked up until the initiating or start interval at the beginning of thecycle, when it is released and then picked up as above described.

Associated with the line and line repeating relays is a bank of steppingrelays, comprising half-step relay VP and stepping relays lV, 2V and LV.Relay C is picked up at the beginning of each cycle and is maintainedenergized throughout the cycle as long as impulsing continues. In theevent of a trouble condition, which causes the system to stop with theline deenergized, relay 0C is released for restoring the system tonormal.

Relay FC is the station start relay, this relay being picked up when thesystem is initiated from a field station and stuck up throughout thesucceeding cycle, it then being released during the clearing out periodat the end of the cycle.

Relay IE is an indication impulse relay, being operated during anindication cycle for applying energy to the line circuit from. linebattery LB. Resistance R is for the purpose of providing a uniformcircuit path for energizing relay FP, under conditions when neitherrelay PC nor NC is connected in series with relay FP.

Positive negative relay PN and retest relay RT cooperate in providingthe indication code, as will be explained in detail. Transfer relay TFand transfer repeater relay TFP are for the purpose of eifecting asecond operation of the stepping relay bank during an. indication cycleonly. Pilot relay lPT is for the purpose of illustrating how the twoindication codes per step are distinctively registered.

Most of the relays of Figs. 3, 4, 5, 6 and 7 correspond to similarlyidentified relays in Figs. 1A, 1B, 2A and 2B, but having distinguishingexponents to indicate that they belong to a modification. The purpose ofother relays and apparatus will be explained in detail when consideringthe operation of the circuits with which they are associated.

Field station equipment-The field station illustrated in Figs. 2A and 2Bis typical of all stations of the system and may be adapted for use atany location by merely connecting certain code jumpers in certainpositions to arrange for the desired codes, but for convenience in thedescription it is assumed that this is the first station on the line byreason of the distinctive exponents employed. I

The track switch, switch machine, switch machine ccntrol relay, signalsand signal control relays are not shown on the drawings, since themethod of controlling the track switch and. signals by polar impulsesapplied to the line circuit is immaterial to an understanding of thepresent invention and may be the same as disclosed in Patent No.2,082,544 dated June 1, 1937.

The communication part of the system, to which the present invention. ismore closely related, includes a line relay F of the three-position,biased-to -neutral, polar type, together with its quick acting repeatingneutral relay l' 'P quick acting line repeating stick relay FPS andrepeating relays SA SE and SC all for a purpose which will be pointedout in detail.

The field station includes a bank of stepping relays, comprisinghalf-step relay VP and stepping relays !V and 2V also transfer relay TFv and transfer repeating relay TFP these relays being operated insynchronism with and for a purpose similar to corresponding relays inthe control office. i

Compensating resistance R is employed for the purpose of compensatingfor the line beyond a. sending station, when this sending stationenergizes the line in towards the control oifice for starting the systemand for providing the lookout feature. Relay CH is provided to registera change in any of the tnaflic controlling devices at the station or achange in the position. of the track relay, and the like, so that thesystem may be initiated for the transmission of indications. Theoperating circuits of relay CH have been omitted, it being understoodthat this relay releases in response to a momentary deenergization ofits stick circuit, the manner in which this is accomplished beingdisclosed in Patent No. 1,852,402.

Lockout relay L0 is provided to determine when this field station is totransmit its indications. Whenever the lookout relay is picked up, theassociated field station is permitted to transmit its indications.Station selecting relay S0 is provided for illustrating stationselection for controls, this relay being picked up at the illustratedstation (and at all other stations connected to the system) at thebeginning of a control cycle,

after which those SO relays at non-selected stations are dropped out,with only that one at the selected station remaining picked upthroughout the complete control cycle.

Relay CHP is a repeater of relay CH and its function will be describedin connection with the lookout feature. Resistance IR is a resistancewhich compensates for the resistance of the appli cation or controlrelays which may be connected to bus H9, so that the constants of the FPand SO relay circuits will not vary when the check circuits of theserelays are effective, irrespective of whether the check is effectedthrough a con.- trol relay or not, all of which will be described, indetail later in the description.

Line opening relay OP is for the purpose of providing the line lock andstep check feature, above mentioned, the detailed manner in which thisis accomplished being pointed out later in the description. ResistanceIR cooperates in the operating circuit of relay 0P whereby a contactclosed in the neutral position of line relay F is not required, as willbe apparent from the description of the operation of the line lockfeature. Resistance IR is for the purpose of providing a path fornormally energizing relay FP during the normal condition of the system.

7 Relays PC and N0 are for the purpose of providing the polar indicationcoded impulses,

' by connecting valve RCT in the line in normal and reverse order.Switch machine relay SMR is of the polar magnetic stick type and is forthe.

vided into a number of impulse periods separated by time spaces andthese impulse periods will be referred to as on periods of the cycle,with the time spaces being referred to as off periods of the cycle.

Normal conditions.-The line circuit is normally energized with what maybe conveniently referred to as energization, over a circuit which may betraced from the terminal of line battery LB in the control ofiice, backcontact 23 of relay PC, front contact 2| of relay NC, return lineconductor, through the tie at the end station, back contact I2I-of relayL0 back contact I of relay 0P winding of line relay F line conductor,winding of line relay F, front contact 22 of relay NC and back contact20 of relay PC, to the terminal of battery LB. It will be understoodthat the line circuit includes relays andcontacts at other fieldstations'in the system (when provided), similar to those traced for thefield station illustrated in Fig. 2A.

Relays FF and NC are normally energized in series over a circuitextending from winding of relay FP, contact 24 of relay F in, itslefthand position, back contact 25 of relay C, back contact 26 of relaySC, winding of relay NC, back contacts 21, 28 and 29 of relays VP, IVand2V respectively, to The above described energizing circuit for the lineeffects the energization of relays F, F and the line relays the otherstations connected to the line circuit. Since a energization is normallyapplied to the line circuit, itwill be assumed that current flow in thisdirection over the line is effective to'operate the polarcontacts of theline relays to the left.

Relay SA inv the control office is normally energized over a circuitextending from back contact 32 of relay LV, back contact 50 of relay SB,front contact 34 of relay NC and winding of relay SA, to All otherrelays in the control office are normally deenergized. V

Allrelays at the illustrated field station are deenergized except relaysCH and F energized as previously described and relay FP which isnormally energized over a circuit extending from winding of relay FPcontact I of relay F in its left-hand position, back contact I3I ofrelay 80 front contact I32 of relay CH and resistance'IR, to

Manual start.-For the purpose of considering the operation of thepresent system, it will be assumed that the station illustrated in Figs.2A and 2B is selected in response to the operation of starting buttonSTB of Fig. 1A. It will furthermore be assumed that switch machine leverSML is positioned to the left for controlling the operation of the trackswitch (not shown) at the illustrated station to its normal position.

The actuation of button STB closes an obvious circuit for picking uprelay CH. Relay CH sticks up over a circuit extending from back contact35 of relay CD, front contact 36 and winding of relay CH, to up over acircuit extending from back contact 31 of relay SC, back contact 38 ofrelay FC, back contact 39 of relay C, upper winding of relay LC, frontcontact 40 ofrelay CH, to

Relay LC closes a pick-up circuit for relay C from through a circuitincluding back contact 31 of relaySC, back contact 38 of relay FC, upperwinding of relay C, front contact I80 of I relay LC, to

The picking up of relay C closes a pick-up circuit for the relay CD fromthrough a circuit including back contact 31 of relay SC, back contact 38of relay FC, front contact 39 of relay C, back contact IBI of relay CDS,front contact I82 of relay CH, upper winding of relay CD, to

prevent the picking up of more superior CD relays (not shown) shouldtheir relays CH (not shown) be picked up. 7

The picking up of relay CD shifts the stick circuit of relay CH fromback contact 35, through front contact 35 of the make-before-break type,

back contact SI of relay 2V (or the stepping relay next to relay LV) toThe picking up of relay C, effects the release Relay LC is now picked j1 of relay NC because its previously described energizing circuit isopened at back contact 25 of relay C. Relay PC is now picked up over acircuit extending from winding of relay FP, contact 24 of relay F in itsleft-hand position, front contact 25 of relay C, back contact 42 ofrelay SC, front contact 43 of relay SA, winding of relay PC and over theabove described circuit including the contacts of the stepping relaybank, 1

to at back contact 29 of relay 2V;

The release of relay NC and the picking up of relay PC changes theenergization of the line to a energization by reason of pole changercontacts 20, 2I, 22 and 23. This change in'energization of the linecircuit switches the stick circuit for itself extending from backcontact 32 of relayrLV, front contact 45 of relay FP, front contact 46and winding of relay QC, to This stick circuit is intermittentlyinterrupted by the release of relay FP during the following impulses,but due to the slow acting characteristics .of relayOC, it is maintainedin 1 5 its picked up position as long as these impulses continue at therequired rate.

Relay SA is released because of open front contact 34 of relay NC. Therelease of relay SA effects the release of relay PC, because its abovedescribed circuit is now ope-n at front contact 43 of relay SA. Therelease of relay PC deenergizes the line circuit to mark the end of thestart or initiating period and the beginning of the conditioning offperiod.

The line relays release in response to the dc-.

energization of the line circuit and relay FF is released becausecontact 24 of relay F assumes its neutral position. Relay SA is nowpicked up over a circuit extending from back contact 41 of relay FF andwinding of relay SA, to Relay SB is picked up over a circuit extendingfrom front contact 48 of relay 0C, back contact 49 of relay FP, frontcontact 58 of relay SA, and winding of relay SB, to Relay SC is pickedup over a circuit extending from back contact 32 of relay LV, frontcontact 5!! of relay SB .and winding of relay SC, to

Relays C and LC remain stuck up in multiple over a circuit that wascompleted by the picking up or relay OC and which extends from backcontact 32 of relay LV, front contact 5| of relay 00, back contact 52 ofrelay FC, front contact 53 and lower winding of relay C, to andthrough-back contact 52 of relay FC, front contact 4| of relay LC, lowerwinding of relay LC, to

The picking up of relay SC closes a circuit for picking up relay PCwhich extends from front contact 55 of relay SC, front contact 54 ofrelay C, back contacts 58 and 59 of relays 2V and IV respectively, frontcontact 60 of relay CD, code jumper I3, winding of relay PC and over theabove described circuit including the contacts of the stepping relaybank to at back contact 29 of relay 2V. This picking up of relay PCmarks the end of the conditioning off period and the beginning of thefirst on period.

I mpulsing and stepping operatz'0ns.When relay PC picks up to mark thebeginning of the first on period, as previously described, aenergization is applied to the line circuit for actuating the polar linerelays to the right. Relay FF is now picked up over a circuit extendingfrom Winding of relay FP, contact 24 of relay F in its right-hand dottedposition, front contact 64 of relay C, front contact 42 of relay SC andresistance R, to

Relay VP is now picked up over a circuit extending from front contact55of relay OC, front contact 55 of relay SB, front contact 61 of relay FP,back contacts 18 and 1! of relays 2V and 5V respectively, winding ofrelay VP and back contact 286 of relay TF, to Relay VP closes a firststick circuit for itself extending from front contact 55 of relay 0C,front contact 56 of relay SB, front contact 12 of relay VP and backcontacts 19 and H to the winding of relay VP.

Relay PC is now released, because of open back contact 21 of relay VP,which marks the end of the first fon period and the beginning of thefirst off period, by deenergizing the line circuit. The line relaysrelease in response to the line circuit deenergization and relay FF isreleased because of open contact 24 of relay F.

A second stick circuit is now closed for relay VP which extends fromfront contact 55 of relay OC, front contact 65 of relay SB, back contact61 of relay FP, front contact 13 and winding of relay VP and backcontact 280 of relay TF, to Relay IV is now picked up over a circuitextending from front contact 65 of relay 00, back contact 15 of relayFP, front contact 14 of relay SB, front contact 16 of relay VP, backcontact 18 of relay 2V, winding of relay IV and back contact 280 ofrelay TF, t0 Relay IV is stuck up over a circuit extending from frontcontact 65 of relay 00, front contact 19 and winding of relay IV andback contact 28!! of relay TF, to At this time it will be pointed outthat the other stepping relays 2V and the like, are stuck up, whenpicked up, over a similar circuit including their front contacts 80, andthe like.

Relay NC is not picked up over a circuit extending from front contact 55of relay SC, front contact 54 of relay C, back contact 58 of relay 2V,front contact 59 of relay IV, front contact 83 of relay CD, code jumperI4, winding of relay NC, front contact 21 of relay VP, front contact 28of relay IV and back contact 29 of relay 2V, to

The picking up of relay NC applies a energization to the line circuitfor actuating the line relays to the left. over a circuit extending fromwinding of relay FP, contact 24 of relay F in its left-hand position,front contact 25 of relay C, front contact 42 of relay SC and resistanceR, to

Relay VP is now released because its first stick circuit is open at backcontact H of relay IV and its second stick circuit is open at backcontact 61 of relay FP. Relay NC is now released because .of open frontcontact 21 of relay VP.

The release of relay NC deenergizes the line to mark the end of thesecond on period and the beginning of the second off period, at whichtime the line relays are released. Relay FF is released because of opencontact 24 of relay F.

Relay 2V is now picked up over a circuit extending from front contact 65of relay 0C, back contact 15 of relay FP, front contact 14 of relay SB,back contact 16 of relay VP, front contact 85 of relay IV, winding ofrelay 2V and back contact 280 of relay TF, to

Relay PC is now picked up to apply a energization to the line to markthe end of the second o period and the beginning of the third on period,resulting in the picking up of the line relays. The circuit for pickingup relay PC extends from front contacts 54 and 55 of relays C and SC,front contact 58 of relay 2V, front contact 86 of relay CD, lever SML inits left-hand position, Winding of relay PC, back contact 21 of relay VPand front contact 29 of relay 2V, to

In response to the energization of the line and the picking up of theline relay in the oflice, relay FP is picked up over the previouslydescribed circuit including contact 24 of relay F in its right-handdotted position. Relay VP is now picked up over its previously describedcircuit, but which now extends through front contact 10 of relay 2V andfront contact 61 of relay FP. The

Relay FF is now picked p circuit is closed for relay LV which extendsfrom front contact 81 of relay SB, front contact '88jand upper windingof re1ay LV, to

It is to be noted that the picking up of stepping relay 2V (orthestepping relay next to relay LV, in case there are a greater numberof stepping relays), opened the stick circuit forrelay CI-I. So that theopening of back contact 32 of relay LV ,deenergizes the stick circuitsfor relays C and LC so that these relays are released and open the stickcircuit for relay CD at front contact I83. Relay SC is also released atthis time because of open back contact 32. Since relay LV does notselecta. channel. circuit'for controlling the PC and NC relays, neither ofthese relays is picked up during the clearing out period to againenergize the line, consequently relay FP remains down and the stickcircuit for relay 00 remains deenergized, at open front contact of relayFP, for a sufilcientlylong interval of time to allow relay O0 torelease. 7

The release of relay OC and the consequent opening of its front contact65 effects the release of all of the stepping relays, except relay LV,but including relay VP. The opening of front contact 48 of relay 0Cdeenergizes relay SB and this relay releases after an interval of timemeasured by' its slow acting characteristics. It will first be assumedthat no oflice start condition is stored at this time, therefore thesystem goes into its normal condition with relay SA'remaining picked up.This isbecause relay SA remains energized, at back contact 41 as long asrelay FP is down, then relay NC is picked up to complete the abovedescribed normal energizing circuit for relay SA at front contact 34before SA has time to release. 7

Relay NC is picked up during the "clearing out? period, after thestepping relays have released and afterrelays SC, C and 00 havereleased, but before relay SB releases, over a circuit extending fromwinding of relay FP, front contact 89 of relay SB, back contact 90. ofrelay 00, back contact 25 of relay C, back contact 26 of relay SC,winding of relay NC, back contacts 21,

2B and 29 of relays VP, IV and 2V, to This circuit also effects thepicking up of relay FP.

With relay NC thus energized, a energization is applied to thelinecircuit for actuating the polar line relays to the left, which completesthe above-described normal energizing circuit for relay NC at contact 24of relay F in its left-hand position. This energization of the linerestores the system to its'normal condition, relay LV being releasedwhen relay SB releases, as previously mentioned, to open the stickcircuit for relay LV, at front contact 81.

Polarity selection of impulses .I n the above example, it has-beenpointed out how relays PC and 'NC are picked up to mark the end of anoff" period and the beginningof an off period. Re-

lay NC'isaWays picked up during the clearing out? period to provide thenext normal en- .erg'ization of .the line circuitand relays PC and c NCareselectively picked up to provide or energizations'ofthe line inaccordance with the code jumper connections and lever positions,

' as pointed out in the above example.

- In the event thatjumper I3 is in its alternate steam dotted lineposition, then relay NC is'picked up to make the first on a energizationinstead of a energization. The same applied to jumper I4, which isselected when relay IV picks up during the first off period, forselecting the PC or the NC relay, for determining the polarity of thesecond on period; This operation occurs on each step of the cycle fordetermining the code to be applied to the line circuit, by selecting thePC or the NC relay during off periods,

for determining whether the line will be energized with a or a impulseduring succeeding on periods. I

.It will be understood that this arrangement may be extended for as manysteps as'desire'd,

conditions, since the above typical example will 7 indicate how such aselection is provided. 7

Line lock, step check and station selection.-As above explained, linerelay F at the illustrated field station responds to the on and offperiods the same as line relay F in the control of fice. During theinitiation part of the cycle, when relay F is shifted from its left toits right-hand position, relay S0 is picked up over a circuit'extendingfrom winding of relay FP contact !3II of relay F in its right-handdotted position, back contact II2 of relay SC and upper winding of relayS0 to ()L A stick circuit is now closed for relay S0 extending from backcontact I I3 of relay FPS back contact I15 of relay SB front contact'lll and lower winding of relay S0 to When relay F releases, at thebeginning of the conditioning ofFperiod, relay FP (normally energized aspreviously described), releases because of open contact I30 of relay Fis now picked up over a circuit extending from back contact H5 of relaySE back contact I I6 of relay FP Winding of relay 0P and resistance IEto 7 Relay SA is picked up overa circuit extending from back contact I"of relay FP back contact II8 of relay SB and winding of relay SA to ll!of relay SAE the above described stick circuit for relay S0 ismaintained complete by bridging back contact I15 of relay SE Relay SB isnow picked up over an obvious circuit closed at front contact H9 ofrelay SA and relay SC is picked up over an obvious circuit completedthrough front contacts I22 and I23 of relays SA and S3 Due to the slowacting characteristics of relay SA it will not be released when itscircuit is opened at back contact H8, because of a stick circuitcompleted imme-.

diately thereafter by the picking up of relay FP and theconsequentclosure of its front contact I I I, which stick circuit includes frontcontact I 24 of relay SA I The picking up of relay GP, in response tothe opening 'of the linecircuit in the control office, opens up the linecircuit at the field station at back contact I20, Relay OP is releasedwhen relay SB picks up and opens its back contact I I5. The release ofrelay OP and the consequent closure of its back contact I20 closes upthe line circuit at the field station. It will thus the line in theofiice and does not'release to close Relay 0P At front contact 7 up theline at the station until conditioning at the station has been completedby the picking up of relay SE Relay P performs this same function duringeach off period as will be described.

At the beginning of the first on period, the picking up of relay Feffects the picking up of relay FP over a circuit extending from windingof relay FP contact I30 of relay F in its right-hand dotted position,front contact IIZ of relay 50 front contact I26 of relay S0 backcontacts I29 and I33 of relays 2V and IV respectively, code jumper I34in its full line position, resistance IR front contact I35 and upperwinding of relay S0 to This pick-up circuit for relay FP includes theselecting circuit for relay S0 so that relay S0 remains energized bymeans of this selecting circuit, completed before relay FPS picks up andopens its back contact II3 to open the stick circuit for relay S0 aswill now be described.

Relay FPS is picked up over a circuit extending from front contact I36of relay S0 back contact I31 of relay 0P contact I38 of relay F in itsactuated position, back contact I39 of relay OP and lower Winding ofrelay FPS to It will thus be seen that the picking up of relay FPS in anon period is dependent on relay S0 being picked up and relay 0P beingdown. Relay F'PS is stuck up over a circuit extending from front contactI36 of relay S0 back contacts I 42, I43 and I44 of relays 2V IV and VPrespectively, front contact I45 and upper winding of relay FPS to Aspreviously mentioned, the picking up of relay FPS and the consequentopening of its back contact I I3 breaks the temporary stick circuit forrelay S0 so that relay S0 is dependent for its energization on theselecting stick circuit, including code jumper I34 and contact I30 ofrelay F in its right-hand dotted position, since relay VP has not yetpicked up to close its front contact I68.

Relay VP is now picked up over: a-circuit extending from front contactI03 of relay SA front contact I25 of relay FP back contacts I43 and I49of relays 2V and IV respectively, winding of relay VP and back contact I14 of relay TF to The first stick circuit for relay VP is completed atits front contact I00, which is independent of the position of contactI25 of relay FP The above described stick circuit for relay FPS is nowopened at back contact I44- of relay VP so that the continuedenergization of relay FPS is now dependent on the circuit through itslower winding, which includes contact I38 of relay F Itwill thus be seenthat relay FPS when picked up, cannot release in response to an off"period and the consequent release of relay F unless the previous on stepwas taken, that is, relay VP must have picked up and opened the stickcircuit of relay FPS including its upper winding.

During the first off period, the release of relay F effects the release.of relay FP because of open-contact I30. Relay FPS is now releasedbecause of open contact I38. Relay OP has energy applied to itsright-hand terminal as soon as relay VP picks up, over a circuitextending from front contact 536 of relay S0 back contacts I42 and I43of relays 2V and IV respectively, and front contact I0! .of relay VP Atthis time, energy is applied to the lefthand terminal of relay OP over acircuit extending from front contact I36 of relay S0 back contact I31 ofrelay CP and contact I38 of relay F in its actuated position. When relayF releases, at! the beginning of the o period, the opening of contactI38 removes from the left-hand terminal of relay 0P so that this relayis picked up over the previously described circuit extending from to itsrighthand terminal, through the Winding of relay OP and resistance IR toIt will thus be seen that relay OP is picked up immediately after therelease of relay F without the use of a contact closedby the release ofthis relay.

When relay FPS releases in the first off period, the above describedcircuit for relay S0 is again closed at back contact H3. The release ofrelay FP during the first off period closes a secondstick circuit forrelay VP extending from front contact 503 of relay SA back contact I25of relay FP front contact I02 of relay VP and Winding of relay VP andback contact I14 of relay T, to

Relay IV is picked up during the first off period over a circuitextending from front contact I06 of relay SA front contact I04 of relay0P front contact I05 of relay VP back contact I01 of relay 2V winding ofrelay IV and back contact I14 of relay TF to Relay IV is stuck up over acircuit extending from front contact I03 of relay SA front contact I08and Winding of relay IV and back contact I14 of relay TF to It Will bementioned at this time that similar stick circuits are completed atfront contacts of relays 2V and the like, when these relays are pickedup.

Since relay FPS is down and is removed from the right-hand terminal ofrelay 0P at open front contact H3 and since relay IV is up and isremoved from the right-hand terminal of relay 0P at back contact I 43,relay OP is released. It will thus be seen that relay 0P picks up inresponse to the line deenergization at the beginning of the first offperiod, to further open the line at back contact I20 and that this relayis not released to close up the line at this station until the step istaken, that is, until relay IV picks up.

Since this same operation is effective during the following off and onperiods, it is believed unnecessary to point out the circuits in detail,it being obvious how these circuits are controlled from the abovedescribed typical examples during the conditioning "off period andduring the first off period. From the above examples it will be apparentthat relay VP is controlled by relay PP and that the F relays arecontrolled by relay 0P When relay FPS picks up during the second onperiod, due to the previously described circuit being closed at contactI38 of relay F the temporary stick circuit for relay S0 is opened atback contact H3. Relay S0 is now dependent for its energization on acircuit including a contact closed by relay F (which was necessarilypicked up before relay FPS was picked up), which circuit extends fromwinding of relay FP contact I30 of relay F in its left-hand position(since the second impulse was front contact I3I of relay S0 frontcontact I09 of relay S0 back contact I52 of relay 2V front contact I53of relay IV code jumper I54 in its full line position, resistance 5Rfront contact I35 and upper winding of relay S0 to 7 It will thus beseen that the combination of and impulses applied to the line cir-.

which in the present embodiment is assumed to be during the first andsecond on periods, as

- determined by the positions of jumpers I3 and I4 in the controloffice, effect the continued en- 'ergization of relay S at theillustrated field station. The-circuits for the other field stations aresimilar, the difference beingin the positions of the station codejumpers (not shown), which serve to condition selecting circuits for theasso-V ciated'SO relays so that only one of these relays will remainenergized after the receipt of the last station selecting code impulse.

For example, at a station having a code jumper similar to I34 connectedin its dotted line position, the first energization of the line wouldfail to complete a selecting stick circuit for the associated SO relaybecause the polar contact of the line relay, similar-to contact I30,would be actuated to the rightand the above described selecting stickcircuit would be open at the code jumper connection. Similarly, if thefirst impulse applied to the line is then relay- S0 at the illustratedfield station would be deenergized because contact I30 of relay F isactuated to the left, so' that the selecting stick circuit for relay S0is open at jumper I34.

With relay SO down, the next energization of the line is ineffectivetocomplete a circuit for picking up relay $0 but FP is picked up 'over acircuit extending from winding of relay discontinued and the linecircuit is not opened trol relay SMR are connected to bus I I0. This 7is for'the purpose of checking the continuity of at a station, after itfails to be selected. The associated line relay continues to operate inresponse to the impulses applied to the line and at contacts similar toI30, the associated FP relays are controlled over circuits extendingthrough a resistance similar to IE The operation of the FP relays atnon-selected stations maintains the SA, SB and SC relays energizedduring the remainder of the cycle.

It will be seen that the windings of switch conthe channel circuitsselected after the station selection portion of the cycle, as well asthose selected during stationselection. Recalling that the third onperiod was because of the position of lever SML in the oifice, theactuation of the contacts of relay F to the right closes a circuit forenergizingrelayslF'P and SMR. in

' series which extends from winding of relay FP contact I30 of relay Fin its right-hand dotted position, front contact 2' of relay SC frontcontact I26 of relay S0 front contact I29 of relay 2V lower winding ofrelay SMR front contact I35 and upper winding of relay S0 to 'Sincecurrent flows through the lower winding of relay SMR. from right toleft, the

polar contacts of this relay will be positioned to the left forcontrolling the associated switch machine (not shown) to its normalposition, in accordance with the position of. lever SML.

Since the energization'of relays FE and S0 other off periods.

during the third on period is dependent on. a complete circuit includingthe third channel circuit, it will be seen that this checks the circuitconditions at the station. after the station selection steps, because anopen relay winding or an open channel circuit would prevent the pickingup of relay FF and the energization of relaySO by means of its selectingstick circuit. This would result in the release of relay SO as soon asrelay FPS picked up, during this on period, and opened its back contactII3. In the event that lever SML is in its right-hand dotted position,then a impulse is applied to the line during the third on period forpositioning relay F to the left. This closes a circuit through the upperwinding of relay SMR extending from winding of relay FP contact I30 ofrelay F in its left-hand position, front contact I3I of relay'SC frontcontact I09 of relay S0 front contact I52 of relay 2V upper winding ofrelay SMR front contact I35 and upper winding of relay $0 to wise checksthe continuity of the channel circuit at this step and, since the upperwinding of relay SMR, is energized in opposite direction to thatdescribed in connectionwith its lower winding, it positions its polarcontacts to the right for controlling the switch machine to its reverseposition.

In a similar manner, any number of additional steps may be used fortransmit-ting additional controls to the selected field station forgovern"- ing signals and such other devices as may be employed. It willbe noted that the and control channel circuits can only be energized ata station where relay S0 has its front This likecontact I'closed. Thisresults in controls being effective only at a selected station, asdetermined by the associated SO relay being energized.

It is. believed unnecessary to describe additional steppingoperations,since the V relays pick up and stick during the o periods, ma mannersimilar to that described in, connection with relay IV and also similartothe V relays in the control office. Likewise, relay VP is released and7 picked up in a manner similar to that described inconnection withrelay VP in the control office.

' The field station is restored to normal during the clearing outperiod, by the release of relay F in response to the deenergization ofthe line circuit, which effects the release of relays FP and FPS becauseof open contacts I30 and I38, as previously described. Relay 0P picks upduring this clearing out period, the same asin Relay FP remains downlong enough during the (clearing out period to c release relay SAbecause of open front contact I I1; Relay SE is. stuck up during theclearing out period over a circuit including back contact I II of relayFP and front contact I58 of relay SE but relay SC is released when relaySA opens its front contact 122., I

The release of relay SA and the consequent opening of front contacts I03and Ifideffects the release of the stepping relays, after which relay OPis released because of open front contact I I 3 of relay FPS and becauseof open front contact I36 of relay S0 The sticking and the release ofrelay S0 will now'be explained more in detail. During anon period,the'energization or" relays S0 and FP. are both dependent on a'completedchannel c'ircuit. If an open channel circuit is encountered, neither S0nor FP can pick up, resulting in the dropping out of this station, aspreviously described.

During each on relay FPS opens its back contact H3 to break the stickcircuit for relay S0 but its selecting stick circuit is completed aheadof this. This completed selecting stick circuit picks up relay FP andshifts relay VP Therefore, the picking up of relay VP in the first oncompletes a stick circuit for relay S0 at front contact H38, which isopened in the first off at back contact liil, but not until after relayFPS has released to complete the stick circuit at back contact I It.This same operation applies to other steps.

During the clearing out period, relay 8A is down with its front contactill open, while relay SE is up with its back contact 575 open, so thatthe stick circuit for relay S0 is incomplete and, since this is an offperiod, its upper winding is open at contact I33 of relay F and also atfront contacts H2 and ifil of relay SS Relay S0 is thus released.

When the line is reenergized at the end of the clearing out period inthe offi-ce, as previously described, effective when relay 0P hasreleased and. closed its back contact l2ll, relay F positions itscontacts to the left and relay FP is picked up over its previouslydescribed normal energizing circuit. Relay SE is released by the pickingup of relay FP and the consequent opening of its back contact ill.

Transmission of indications.-A change in the condition of the tracksection or a change in the condition of the traiiic controlling devicesat the field station, effect the deenergization of relay CH which closesa circuit for picking up relay Cl-IP extending from winding of relay FPcontact I of relay F in its left-hand position, back contact 131 ofrelay S0 back contact 632 of relay CH and upper winding of relay CHP toCHIP closes a stick circuit for itself extending from (-1-), backcontact of relay SE front contact i5! and lower winding of relay CHP toRelay OP is now picked up, over a circuit extending from front contactH58 of relay Cl-IP back contact I59 of relay L0 winding of relay CP andresistance IE to Relay 0P opens the normally energized line circuit atback contact $20, to mark the end of the normal on period and thebeginning of the starting off period, at which time line relay F in theoffice and the line relays at the field stations are released.

Referring to the control office, relays NC and PP are released becauseof open contact 24 of relay F. The release of relay NC also opens theline in the control ofiice at contacts 2! and 22, thus effecting theopening of the line circuit in the office in response to an open linecircuit condition applied at the field station. The line circuit cannotbe energized until the apparatus in the ofiice and at the station hasresponded, at which time it will be closed at both locations.

Relay FC in the control oflice is picked up over a circuit extendingfrom back contact 32 of relay LJ, back contact i5 of relay FR frontcontact iii of relay SA, back contact of relay SB and lower winding ofrelay FC, to Relay 0C is picked up over a circuit extending from backcont ts an 3 o relays LV, SB and NC, f contact 5i FC and winding ofrelay CC, to Relay SB is picked up over a circuit extending from frontcontact 48 of relay 0C, back contact if? of relay PP, front contact 68of relay SA and winding of relay SE, to Relay SC is picked up over acircuit extending from back contact 32 of relay LV, front contact 59 ofrelay SB and winding of relay SC, to

Relay F0 is stuck up, when relay OC picks up, over a circuit extendingfrom (-1-) back contact 32 of relay LV, front contact 5i of relay 00,front contact 52 and upper winding of relay FC, to It will be seen thatthe picking up of relay FC opens the pick-up circuit of relay C at backcontact 33 and the stick circuit of relay C at back contact 52.

Relay PN of Fig. 1B is picked up during the start off period, over acircuit extending from front contact 971 of relay FC, back contact 98 ofrelay IE and lower winding of relay PN, to Relay RT is now picked upover an obvious circuit closed at front contact 99 of relay PN.

Relay IE is picked up over a circuit extending from front contact ofrelay SC, back contact 54 of relay C, front contact 69 of relay FC,winding of relay IE and back contacts 27, 28 and 29 of relays VP, IV and2V respectively, to With relays PN and IE picked up, energy is appliedto the line over a circuit extending from the terminal of battery LB,conductor l front contact 3% of relay IE, upper inding of relay PN,front contact ll of relay PN, conductor 63 and winding of relay F to theline conductor, with the circuit from the terminal of battery LBextending by way of conductor ill,

front contact 3i of relay IE, front contact 59' of relay PN andconductor 98 to the return line conductor.

Referring to the field station, the release of relay F effects therelease of relay FP 'because of open contact I36 of relay F Relay SA ispicked up over a circuit extending from back contacts Ill and H8 ofrelays FF and S13 and winding of relay 8A to Relay S5 is picked up overan obvious circuit closed at front contact H9 of relaly SA and relay S0is picked up over an obvious circuit closed at front contacts I 22' andI23 of relays 8A and SB Relay L0 is picked up over a circuit extendingfrom front contact Hit of relay S13 winding of relay L0 and frontcontact Hit of relay CHP to Relay PC is now picked up over a circuitextending from front contact Mil of relay L0 back contact Ml of relay TFback contact I of relay 2V back contact ofrelay lV jumper Hi5 andwinding of relay PC to Relay OP is released because of open back contact59 of relay L0 With relay IE in the control ofiice up, with relay 0P atthe field station down and with relay PC at the field station picked up,the line circuit is now given a (-1-) energization over the previouslydescribed circuit extending to the line and return conductors, it beingrecalled that was applied to the line conductor and to the returnconductor. now extends over the line conductor, through relay F backcontact I20 of relay 0P front contact I21 of relay L0 resistance R frontcontact I'M of relay PC back contact H! of relay N0 through valve RCTback contact I12 of relay N0 and front contact I13 of relay PC to thereturn conductor. It will thus be seen that, because of indicationjuniper !46 connected in its full line position. relay PC is picked upto permit the (-1-) energization of the line by way of valve RCT Thisprovides one choice of the two indications which may be transmitted ateach step, the other choice being explained in connection with the seconperiod. I

The energization of theline circuit marks the end of the start offperiod and the beginning of the first on period, at which time the linerelays in the office and at the field stations (up to and including thatstation which initiated the system) position their contacts to theright. Relay FP in the control oilice is picked up over a circuitextending from winding of relay FP, contact 24 of relay F in itsright-hand dotted position, back contact 64 of relay C, front contact I6 of relay SC and resistance R, to Relay VP is now picked up over itspreviously described circuit and its previously described first stickcircuit is completed. Relay IE is released because of open back contact21 of relay VP.

Relays PC and NC in the control ofiice are not operated during anindication cycle, because no CD relay is picked up to complete thecontrol channel circuits and because of open front contact 54 of relayC. The release of relay IE opens the line circuit in the office atcontacts 30 and 3I, to mark the end of the first on period and thebeginning of the first off period.

During the first on period, relay FP is picked up over a circuitextending from winding of relay FP contact I30 of relay F initsright-hand dotted position, front contact I I2 of relay 8C backcontact I26 of relay S0 and resistance IR to Relay FPS is picked up overa circuit extending from frontcontact I64 of relay L0 back contact I31of relay 0P contact I38 1 of relay F in its right-hand dotted position,back 35.

contact I 39 of relay OP and lower winding of relay FPS to Relay FPScloses a stick circuit for itself extending from front contact I64 ofrelay L0 back contacts I42, I43 and I44 of relays 2V IV and VP frontcontact I45 and upper Winding of relay FPS to Relay VP is now picked upover its previously described pick-up circuit and its first stickcircuit is completed, as above described.

The opening of the line by the release of relay IE in the controloffice, to mark the beginning of the first off period, effects therelease of the line relays. Relay FP in the control ofiice is releasedbecause of open contact 24 of relay F and the previously describedsecond stick circuit for relay VP is closed. The previously describedpick-up circuit for relay IV is closed, this relay is stuck up and relayIE is picked up over a circuit extending from front contact 55 of relaySC, back contact 54 of relay C, front contact 69 of relay FC, winding ofrelay IE, front contacts 21 and 28 of relays VP and IV and back contact29 of relay'2V, to

Relay FPS at the field station is released because its pick-up circuitis open at contact I38 of relay F and because its stick circuit is openat back contact I44 of relay VP Relay F? is released, because of opencontact I30 of relay F and relay OP is picked up, when contact I38 isopened to remove the short circuit from the terminals of the Winding ofrelay 0P the circuit for picking up relay 0P extending from frontcontact picks up its OP relay in response to this deene rgization, whichrelay further opens up the line circuit and holds it open until the stephas been taken. Relay IV is picked up and stuck up as previouslydescribed and relay VP is stuck up over its previously described secondstick circuit. Relay OP is now released to close up the line at thestation, because relay IV picked up and opened the above describedcircuit at back conof two indications discussed in the typical examplescan be used at additional steps of the cycle, for transmittingindications on a'choice of two per step.

During the first off period, the picking up of relay IV at the fieldstation selects the second code jumper connection by Way of frontcontact I63 and indication channel circuit No. 2. In accordance with theexample chosen, a circuit is closed for picking up relay N0 extendingfrom front contact I46 of relay L0 back contact I4I of relay TF backcontact I65 of relay 2V front contact I66 of relay IV code jumper I16 inits full line position and winding of relay N0 to Since relay PCreleases when back contact I66 of relay IV is opened, pole changingcontacts I10 to I13, inclusive, are in the opposite positions from thosepreviously described, so that the circuit for energizing the line with aimpulse'is incomplete because of valve RCT This is because relay IEpicks up in the first off period for applying to the line conductor andto the return conductor, as previously described. In this case, however,the circuit through relay F back contact I 20 of relay 0P front contactI2! of relay L0 resistance R back contact I19 of relay PC and frontcontact I12 of relay NC connects to the terminal of valve RCT which willnot permit current to flow through this valve. vents the energization ofthe line.

Since the energization of the line, as previously described, extendedthrough the upper winding of relay PN and its front contact 11, it 'will{be seen that the non-energization of the line effects the release ofrelay PN because its upper Winding fails to be energized and because itslower winding is deenergized at back contacts 98 of relay IE and at backcontact I8 of relay RT. Relay PN therefore releases and changes thepotential applied to the line from to The line is new energized over acircuit which may be traced from terminal of battery LB, conductor II,front contact 30 of relay IE, back contact I9 oi relay PN, conductor 95,return conductor, back contact I13 of relay P0 front contact I1I ofrelay NC valve RCT front contact I12 of relay NC back contact I10 ofrelay P0 resistance R front contact I2I of relay L0 back contact I23 ofrelay 0P winding of relay F line conductor, winding of relay F,conductor 63, back contact 11 of relay PN, lower winding of relay RT,front contact 3| of relay IE and conductor II), to the terminal ofbattery LB. Relay RT is therefore maintained energized by meansofcurrent The station therefore 'prethrough its lower winding afterrelay PN releases and opens its front contact 99.

In response to this energization of the line circuit, the line relaysactuate their polar contacts to the left for controlling the FP relaysand the stepping relays as previously described. During the secondperiod the deenergization of the line effects the release of relay RT,after which it is again picked up when relay PN picks up during the offperiod for preparing for the next 0 period.

It will thus be seen that the line is energized with polar impulsesduring an indication cycle for positioning the polar contacts of relay Fin the control oifice to the right or to the left in accordance withwhether these impulses are or A impulse effects the energization of anindication receiving relay, such as relay IPT over a circuit extendingfrom (3+) contact 84 of relay F in its right hand dotted position, frontcontact 82 of relays FC, back contact 8i of relay TF, back contacts l4and I of relays 2V and IV respectively and winding of relay IPT, to(CN). A impulse positions polar contact 84 to the left for applying (B)to the channel circuit, similar to that above described, for energizingrelay IPT in the opposite direction.

It is not believed necessary to illustrate or describe the transmissionand the reception of additional polar indication impulses, since thesemay be provided as in the above described typical examples and since asmany may be provided as required. It is furthermore believed unnecessaryto illustrate the method of registering the identity of a transmittingstation in the control office in accordance with a code combination madeup of the polar indication impulses, since such station identification,as well as the transmission of indications to the indication receivingrelays associated with the identified station, has been disclosed innumerous applications and is well known to those skilled in the art.

At the end of an indication cycle, the system is cleared out in themanner above described in connection with a control cycle, with relay FCindications are transmitted, the purpose of this feature being toprovide more indication channels, since it has been found in practicethat typical installations require approximately twice as manyindications as controls during each cycle of the system. Since thestation stepping relay bank repeats its cycle by means of circuitssimilar to those shown in the control ofiice, it is believed unnecessaryto describe the stepping operations at the station.

Relay TF (see Fig. 1B) is picked up during the third off period over acircuit extending from front contact 55 of relay 00, back contact 25 ofrelay FP, front contact 14 of relay SB, front contact '16 of relay VP,front contact 78 of relay 2V, front contact ll of relay FC, back contact3 of relay TFP and winding of relay TF, to Relay TF is stuck up over acircuit extending from front contact 3 of relay 0C, front contact I andwinding of relay TF, to The VP and the V relays are now released becauseof open back contact 280 of relay TF. Relay TFP is picked up over acircuit extending from back contact 28! of relay 2V, back contact 282 ofrelay IV, back contact 283 of relay VP, front contact 284 of relay TFand winding of relay TFP, to Relay TF1? is stuck up over a circuitextending from front contact 8 of relay 00, front contact 288 andwinding of relay TFP, to

Relays TF and TFP remain stuck up until relay OC releases and opens itsfront contact 8 during the clearing out period. Since the V and VPrelays must be down to effect the picking up of relay TFP, may beapplied to their windings at front contact 285 of relay TFP so that theycan be sequentially operated through another cycle by means of theirpreviously described circuits, except now the is applied to theirwindings by way of front contact 285 instead of back contact 280. Theswitching of contact 8! of relay TF from its back to its front pointswitches the indication registering circuit from the lower numberedgroup of channel circuits to the higher numbered group of channelcircuits. It will thus be seen that a channel circult is selected in onegroup at each step of the stepping relay bank and after this bank hasstepped through once, an additional channel circuit is selected inanother group by the operation of the stepping relay bank through asimilar cycle.

Lockoutr-ln the event that two or more sta tions have indications readyfor transmission at the same time, the station nearest the controloffice is given preference and that station (or stations) more remotefrom the control oflice is locked out. It will be assumed that thestation illustrated in Figs. 2A and 23 has indications to transmit atapproximately the same time as the next station, assumed to be stationNo. 2.

Relay CH is released to initiate the system from the station, in amanner previously discussed. It will be assumed that relay CH (notshown) is released at the same time.

A circuit is closed for picking up relay CHP extending from winding ofrelay FP contact i 38 of relay F in its left-hand position, back contact[3! of relay SC back contact i32 of relay CH and upper winding of relayCH1, to Relay CHP is stuck up over a circuit extending from back contacti555 of relay SB front contact l5! and lower winding of relay Cl-lP toRelay OP is new picked up over a circuit extending from front contact 53of relay CHP back contact i59 of relay L0 winding of relay 0P andresistance iR to Similar circuits are effective at station No. 2 (notshown) for controlling the CH, CHP and OP relays at this station.

The picking up of relay 0P opens the line circuit at back contact lZU,which effects the release of the line relays at all stations and in thecontrol office. Relays PP and NC are released because of open contact 24of relay F. The release of relay NC further opens the line circuit inthe control cfiice. The release of relay F effects the release of relayFP because of open contact 53% and relay SA is picked up because ofclosed back contact I ll of relay FP Relay SE is picked up because ofclosed front contact lit of relay 8A and relay SC is picked up becauseof closed front contacts 522 and H3.

Relay L0 is picked up over a circuit extending from front contact 565 ofrelay 5B winding of relay L0 and front contact it?!) of relay CHP toRelay OP 'is released to again close up the line at the station by theopening of back contact I59 of relay L The line cannot be energized atthis time however, since it must wait for the control office to gothrough the conditioning period, as was previously described.

Similar operations of the OP, F, FP, SA, SB, SC and LO relays areeffected at the second station, during the starting off period, but theline beyond the first station can not be energized because of open backcontact IZI of relay L0 The line circuit extends through backcontact I20of relay 0P front contact I2I of relay'LO and resistance R so that theabove described operation of relay OP is effective to provide the linelock feature as previously described.

It will be noticed that the dead line for picking up a CHP relay is atthe point where relay F opens its contact I30. This prevents the pickingup of another CHP relay when relay CI-IP picks up, relay 0P picks up andrelay F releases. In the event however, that the second CHP relay ispicked up before this dead line is reached, it becomes necessary torelease the associated lockout relay (at the inferior station) and thisis accomplished by maintaining the associated SB relay stuck up duringthe open circuit condition of the line, by way of a circuit similar tothat extending through back contact III of relay FP and front contact II8 of relay SB Since a contact similar to back contact H8 of relay S13is open and since a contact similar to front contact i ii of relay FP isopen, the associated SA relay is released which opens the stick circuitof the associated CHP relay at a contact similar to front contact I63,the contact similar-to back contact E58 of relay SB being open.Therefore, at the inferior station, the release of the associated CHPrelay and the consequent opening of its front contact similar to I60effects the release of the associated lockout relay. V

The SB relay at the inferior station remains V stuck up until the systemis restored to normal and the line circuit is reenergized, after whichthe associated CHP relay is again picked up over a circuit similar tothat extending through contact $30 of relay F in its left-hand position,back contact I3I of relay SC back contact I32 of relay CH and upperwinding of relay CHP to It will thus be seen that the inferior stationgets achance to obtain active access to the communication system againand the circuits function as above described to give the next superiorstation control of the line and to lockout any other inferior stationthat may be attempting to transmit its indications.

Stepping is not effected at an inferior station, under the aboveconditions, because of open front contacts I36 of relay SO and openfront contact I64 of relay L0 At a station nearer the office than theone which obtains access to the communication system, the line relaywill be intermittently operated in response to the impulses and theassociated FP relay will be intermittently operated because of a circuitcompleted for the FP relay, by way of a'contact Simi! tion because ofopen front contacts I36 and IM of relays similar to S0 and L0 Storedcontrol conditions-As previously mentioned, the control office haspreference to initiate the system, when it has a stored controlcondition at the time the system goes through its clearing out period.

When relay C is released during the clearing out period, as previouslydescribed, a stored oflice start is eifective to pick up relay LC overthe previously described circuit including back contact 39 of relay C.The CD relay that was up during the previous cycle, is released whenrelay C releases and opens its front contact 62. Relay C is again pickedup over the previously described circuit including front contact H ofrelay LC.

It will be understood that the LC relay now being discussed may beassociated with another starting button and another station, so that theclosure of a front contact similar to BI is effective to pick up theassociated CD relay.

After the stepping relays have been released during the "clearing outperiod, as previously described, relays PC and FF are picked up over acircuit extending from winding of relay FP, front contact 89 of relaySB, back contact 90 of relay OC, front contact 25 of relay C, backcontact 42 of relay SC, front contact 43 of relay SA, winding of relayPC and back contacts 21 to .23 inclusive of the stepping relay bank, to

This picking up of relay PC applies a energization to the line beforethe SA or SB relays have released, but after the SC relay'has released.This energization of the line positions the contacts of the line relaysto the right, which prevents the picking up of a station CHP relay,because the line relay contacts similar to contact I30, must be in theirleft-hand positions for picking up an associated CHP relay.

After the release of relays SB and SA, due to the release of relay 0Cand the consequent opening of its front contact 48, relay PC is released7 because of open front contact 43 of relay SA, to mark the end of thestarting period and the beginning of the conditioning off period, atwhich time the line is deenergized and the system steps through thecycle as before. Relay 0C is picked up when relay LV releases and closesits back contact 32, the circuit being by way of back contacts 50 and 34and front contact 44, as previously described. Relay LV is not releasedat the time the other stepping relays release, its stick circuit notbeing energized until relay SB releases and opens its front contact 81.

In the event of, simultaneous office and field start conditions, whenthe system is in its normal condition, then the field station is givenpreference. since an open circuit start condition, effected by a fieldstation is superior to a change in polarity of energization of the linecircuit, effected by the control oflice.

For example, the release of relay CH effects the picking up and thesticking of relay CHP after which relay OP is picked up to open the lineat the station, all as previously described. In response to the openline condition, relays F, F1? and NC in the office are released andrelay FC is picked up. The opening of back contact 38 of relay FCprevents the picking up of relay C (which controls thetransmission ofcontrols) that the succeeding cycle is marked for the transmission ofindications. Even though relay C is up at the time relay F0 is picked upin response to a field start, the opening of back contact 52 of relay Copens the stick circuit for relay C and since its pick up circuit isalso open at back contact 38, relay C will be released.

Since it requires a line energization at the start of a cycle to pick upan S relay and since a field start condition opens the line forpreventing this energization, no SO relay will be picked up at the startof an indication cycle.

The clearing out operation for an indication cycle is the same aspreviously described in connection with a control cycle and it isbelieved unnecessary to again point out the sequence of operationsduring this portion of the cycle.

Wheatstone bridge indicafions.ln my prior Patent No. 2,068,931, a methodof transmitting indications in a centralized ,traffic controlling systemwas disclosed, comprising circuit means for unbalancing or leavingbalanced a Wheatstone bridge circuit, having the line in one armthereof. The modification illustrated in Fig. 3, is an improvement overthe system in the above patent, in that indications are transmittedbyover-balancing and under-balancing a normally balanced Wheatstonebridge circuit, having the line in one arm thereof. The presentarrangement is an improvement over the prior disclosure, since theindication executing circuits in the control office are much simpler,because the usual line relay is actuated to the right or to the left inaccordance with the over-balance or under-balance of the bridge forapplying (3+) or (B) to the indication channel circuits selected.

3 illustrates only a sufficient portion of the circuits to indicate themethod of transmitting by the over-balance and under-balance Wheatstonebridge arrangement. It is assumed that the system is in its normalcondition, with the line energized by way of the pole changing contactsof the PC and NC relays, the energy being supplied from battery LB whichcorresponds to the line battery LB of Fig. 1A. The path over which theline is energized includes line relay F corresponding to relay F of Fig.2A, and back contacts 323 and Hi of relays OP and L0 which correspond toback contacts I20 and [2| of Fi 2A.

Relay F0 corresponding to relay FC of Fig. 3A., is picked up when thesystem is started from the field station, in response to the opencircuit .tion of the line, in the manner previously described.

Each time that relay IE (corresponding to relay IE of Fig. 1A) is pickedup to apply energy to the line circuit, front contacts 330, 33!, and 333are closed to include the line and resistance a, c, and d in aWheatstone bridge circuit, as more clearly indicated in Fig. 7,corresponding resistances and relays in Figure 7 having exponent 4applied, it being understood that these resistances and relayscorrespond to similar resistances and relays of Fig. 3.

It will first be assumed that, when relay'IE sets up the above describedcondition, the code jumper 346 at the field station is in the positionillustrated in Figs. 3 and 7. This removes resistance R from the lineand it is assumed that the constants of the line circuit, the linerelays and the resistances are such that, under this condition the lineis under-balanced, that is, more current flows through the arm of thebridge in which resistance R is connected, than in the arm in whichresistance a is connected. In other words, with resistance R removedfrom the line,

the product of the resistances in the upper right and the lower leftarms of the bridge is substantially greater than the product of theresistances in the upper left and the lower right arms of the bridge.This causescurrent to flow through line relay F from the right to theleft to apply (B-) at its polar contact 384 to the selected channelcircuit, which circuit may be selected as in Fig. 1A.

The alternate connection of jumper 346 inserts resistance R in the lineand when the Wheatstone bridge circuit is established by relay IEapplying energy to the line, the bridge is overbalanced, that is, theproduct of the resistances in the upper right and the lower left arms ofthe bridge is substantially less than the product of the resistances inthe upper left and in the.

lower right arms of the bridge. This causes cur rent to flow throughrelay F from left to right and (3+) is applied to the selected channelcircuit by way of polar contact 384.

When such an arrangement is used, it is desirable to periodically make atest of the resistance of the line and compensate for variations in thisresistance effected by variations in temperature and the like. Thecircuit illustrated in Figs shows such a compensating arrangement and,in this circuit the system is assumed to be in its normal condition withrelays FP, AX and N0 normally picked up over a circuit extending fromwinding of relay FPflcontact 324 of relay F in its left hand position,back contacts 425 and 426 of relays C and S0 winding of relay AX andwinding of NC to Under this condition the circuits are as illustrated inFig. 5, that is, the line is energized over a circuit extending from theterminal of the battery, back contact 623 of relay P0 front contact 125of relay NC, return line conductor, balancing resistor BB back contact408 of relay L0 line conductor, winding of relay F front cont-act ofrelay NC, back contact 420 of relay P0 and resistance d to the terminalof the battery. A,

Another circuit may be traced from the terminal of the battery, backcontact 323 of relay P0 front contact 42l of relay N0 balancing resistora front contact 432 of relay AK and resistor 0 to the terminal of thenection through front contact 402 of relay AX to resistor a The otherterminal of relay EAL is connected to point Z between resistor 11 andline relay F This connection may be traced by way of front contact 403of relay AX to the winding of relay F and by way of front L contact 422of relay N0 and back contact 42!] proximately equal to the product ofthe'resistm ances in the upper left arm and the lower right arm. Underthis condition the bridge is balanced and no current flows between theterminals Y and Z. Relay BAL therefore maintains its polar contact 635in its neutral position as long as the line contains the properresistance to approximately balance the bridge.

If the line circuit resistance increases or decreases, polar contact 405of relay BAL will be operated to one position or the other forcontrolling (by means of a circuit not shown but" indicated by dottedline .401), resistor 11 to in-' tact on a relay, such as relay BAL,which controls this device. I

Front contacts 406 and 401 of relay IE are for the purpose of setting upthe circuit condition illustrated in Fig. 7 during the transmission ofindications, when the line is energized by the picking up of relay IE Itwill be observed that balancing relay BAL is removed fromthe line duringthetransmission of indications, because relayAX releases and opens thecircuits to relay BAL at front contact 403. Relay AX is released whenrelay F opens contact 424 at the start of an indication cycle (or acontrol cycle) and the circuit to relay. AXtis maintained open at backcontact 426 of relay The circuit for operating relay NC is thencompleted as in Fig. 1A, as indicated by the arrow and the note in Fig.4 ,(to NC selection).

During the transmission of controls the Wheat- 7 stone bridge circuit isnot made up, as indicated in Fig. 6. This is because relay IE does notpick up during a control cycle, so that the only completed circuit fromthe line battery is that indicated in Fig. 6 and it extends over theline circuit, but includes resistor (1 Fig. 8 illustrates the receptionof indications by means of vacuum tubes of the gas filled, arc dischargetype. Instead of relay F being connectedbctween points Y and Z as inFig. '7, re-

sistor R is connected between points Y and Z in Fig. 8. Recalling thatan over-balance of the bridge causes current to flow from .Y to Z andthat an under-balance of the bridge causes current to flow from Z to Y,it will be apparent that current is thus caused to flow through resistor-R in one direction under one indication condition and in anotherdirection under another indication condition.

The input circuit of tube ,TP is connected of this tube and relay MN ispicked up for applying (B-) by Way of front contact 456 to the selectedchannel circuit. Since tubes of this type require some means ofquenching after they are fired, relay IE (corresponding to relay IE ofFig. 4) connects energy to the tube plate circuit at front contact 451,during the time that this relay is picked up for energizing the line andremoves energy from the tube plate circuits by opening front contact45'! to quench the fired tube after the indication transmission period.

Although one specific embodiment of the invention has been shown, itisto be understood that various re-arrangements may be made and still comewithin the scope of the. invention.

Having thus described a centralized trafiic controlling system as oneembodiment of the present invention, it is desired to be'understood thatthis form is selected to facilitate in the disclosure rather than tolimit the number of forms which the invention may assume and it isfurther to be undertsood that various modifications, adaptations andalterations may be applied to the specific form shown to meet therequirements of practice, without in any manner departing from thespirit or scope of the invention, except as limited by the appendedclaims.

What I claim, is: 1. In a centralized trafiic control and indica tionsystem of the selector type for transmitting controls to or indicationsfrom any one of a plurality of field stations at one time; thecombination with an office and a plurality of field stations; a lock-outrelay at each field station; a polar line relay at each field station; aline opening relay at each field station; a line circuit exdendingthrough the line relay, a contact of said line opening relay and a backcontact of the lock-out relay of each field station in succession inaccordance with the distance such field station is from said o-flice andback over a return Wire; a bridge partial circuit at each field stationconnecting the front contact of said lockout relay contact for thatstation to the return wire; means in said office fornormally energizingsaid line circuit with current of a particular polarity; means at eachfield station responsive to. a changed condition at such station foractuating said, lineopening relay and opening said line circuit, saidlast mentioned means being effective only if said line circuitwasenergized with current of said particular polarity and said polar linerelay assumed a particular position .to reclose said line circuit; andmeans at said ofiice for changing the polarity of energization of saidline circuit when said line circuit isto be used for transmittingcontrols from said office.

2. In a centralized traflic indication system of the selector type fortransmitting indications from any one of a plurality of field stationsat one time; the combination with an office and a plurality of fieldstations; a lockout relay at each field station; a polar line relay ateach field station; a line opening relay at each field station; a linecircuit extending through the line relay, a contact of said line openingrelay and aback contact of the lock-out relay of each field station insuccession in accordance with the distance such field station is fromsaid office and back over a return wire; a bridge partial circuitincluding indication impulse creating means at each field stationconnecting the front'contact of said lock-out relay contact for thatstation to the return wire; means in said office for normally energizingsaid line circuit with current of a particular polarity; means at eachfield station responsive to a change condition at such station foractuating said line opening relay and opening said line circuit, saidlast mentioned means being effective only if said line circuit wasenerized with current of said particular polarity and said polar linerelay assumed a particular position when said changed condition becameexist-' ent; means for energizing the lock-out relay at

